https://escholarship.org/content/qt6p3188fd/qt6p3188fd.pdf?t=p0him6

Electrochromic materials and devices for energy-efficient windows

Physical Concepts of High‐Field, Thin‐Film Electroluminescence Devices

Structural and electrical properties of rf‐sputtered amorphous BaTiO3 thin films grown on water‐cooled substrates have been investigated. The dielectric and electrical properties have been studied for films grown under varying sputtering gas composition (Ar+O2 gas mixtures) as a function of film thickness, frequency, and temperature. As‐grown films were amorphous in nature and highly transparent. Post‐deposition annealing had no discernible effect either on film structure or dielectric properties, and there was no evidence of ferroelectricity. Films sputtered in pure argon showed a dielectric constant e’∼12 with little dependence on frequency (0.1–100 kHz) over the temperature range 0–75 °C. The dielectric properties were a function of film thickness and the percentage of oxygen in the sputtering gas during growth. The thickness‐dependent dielectric properties of amorphous BaTiO3 thin films on conducting glass substrates could be satisfactorily explained by a model based on the existence of electrode barriers. The high breakdown voltage (106 V/cm), charge storage capacity (3.1 μC/cm2), and frequency‐ and temperature‐dependent dielectric properties of a‐BaTiO3 films sputtered in pure argon show promise for application as insulating layers in thin‐film electroluminescent display devices.

Structural and electrical properties of rf-sputtered amorphous barium titanate thin films

The use of volatile β-diketonate chelates as precursors for the deposition of thin films for electroluminescent devices is reviewed. Alternating current thin film electroluminescent (ACTFEL) devices consist of an emitting layer sandwiched between two dielectric layers, together with conducting and buffer layers. Besides various physical deposition techniques, the commonly applied methods for preparing thin films are chemical vapor deposition (CVD) and its particular variant atomic layer epitaxy (ALE). Alkaline earth β-diketonates are used as precursors for deposition of the semiconducting alkaline earth sulfide and thiogallate films that provide the matrix in emissive layers, while β-diketonates of lanthanides and a few other metals (Mn, Na, K) are precursors for dopants and codopants producing colors. β-Diketonate precursors can also be used for the preparation of dielectric alkaline earth titanate and oxide layers. Current research on thin film electroluminescent materials is focused on improving the blue color produced by cerium doping of alkaline earth sulfide and thiogallate matrices. The synthesis and properties of β-diketonate chelates and the growth and characterization of the thin films obtained with them are presented and discussed. This review of precursors for TFEL materials is also relevant for other materials, including oxide superconductors.

Volatile Metal β‐Diketonates: ALE and CVD precursors for electroluminescent device thin films

The physical and electrochemichromic properties of the amorphous and crystalline tungsten oxide films prepared by thermal evaporation of WO3 powder under a reducing atmosphere have been investigated. The oxide films with 850–24 500 A thick were deposited on the substrates maintained at a temperature ranging from 50 to 500 °C under a vacuum below 1×10−5 Torr. Properties of the oxide films formed depend considerably on the deposition temperature. The as‐prepared oxide films formed at a temperature higher than 400 °C have a resistivity of 10−3−10 Ω cm, and are blue colored, and mainly composed of crystalline WO3. The oxide films formed at a temperature lower than 350 °C have a resistivity of 105–109 Ω cm, and are transparent and amorphous. Both of the amorphous and crystalline oxide films have good electrochemichromic properties. From x‐ray analysis, the crystalline WO3 thick films were found to change to hydrogen tungsten bronze films with a chemical composition of H0.33WO3 during electrochemical coloration...

Physical and electrochromic properties of the amorphous and crystalline tungsten oxide thick films prepared under reducing atmosphere

AC-coupled thin-film electroluminescent devices employ insulating layers to limit the current density through the active layers. The requirements and limitations in driving such devices are then dependent upon the properties of the dielectric layers. We define an external efficiency for an ac thin-film electroluminescent device and consider two limiting cases, current response 1) fast, and 2) slow, compared to an applied voltage change. Relationships are then derived among external efficiency, relative luminance, and the two principal characteristics of the insulating layer, specifically charge density at breakdown and thickness. It is shown, for example, that charge density at breakdown for the insulators should be at least three times the corresponding quantity for the active layer.

The importance of insulator properties in a thin-film electroluminescent device

Several different types of electrochromic display devices are discussed. Their electrooptical properties and device characteristics are investigated and compared. Performance parameters for these devices are discussed in terms of their applicability to information display. It is concluded that electrochromism is best suited for direct-addressed displays.

Performance characteristics of electrochromic displays

One of the problems inherent in active matrix displays, which can prevent them from achieving gray-scale images of CRT quality, is crosstalk, whereby information is coupled along columns of the display. While alternating data voltages line by line can reduce such crosstalk, it requires a sacrifice of resolution in the displayed image. The authors have developed a scheme for reducing crosstalk by a cancellation technique based also on a change of drive waveforms, but producing no loss of resolution. This approach does, however, require a factor of two increase in bandwidth or switching speeds. The technique can be applied to all types of active matrix displays, including thin-film-transistor, MIM, and diode types. >

Eliminating crosstalk in thin film transistor/liquid crystal displays

Liquid-crystal displays addressed by thin-film transistors are subject to crosstalk associated with parasitic capacitances. An addressing technique that provides compensation for crosstalk, eliminating its visible effects, is described. Each row-addressing time interval is subdivided into two intervals, one of which is used for normal data transfer into the row. During the other subinterval, all gates are inactive, and a compensation voltage that is complementary to the data voltage for the row being addressed is applied to each column. This technique does, however, require a factor-of-two increase in bandwidth or switching speeds. >

Eliminating crosstalk in thin-film transistor/liquid-crystal displays

The pressure dependence of barrier heights in Ge–GaAs n—n heterojunctions has been determined, for hydrostatic pressures up to 28 kbar, by means of electrical measurements. The results, expressed in terms of the pressure coefficient of the conduction‐band discontinuity ΔEc, are d(ΔEc)/dP = (6.7±1.0) meV/kbar for junctions having both (100) and (110) orientations. This result is seen to be in approximate agreement with predictions based upon considerations of bulk band energies only. It is concluded that the pressure dependence of any dipole‐layer contribution to ΔEc can be ignored. The results for d(ΔEc)/dP can then be used to obtain a value of ‐ (6.8±1.0) eV for the dilatational deformation potential for the conduction band of GaAs.

W.E. Howard

Papers

The importance of insulator properties in a thin-film electroluminescent device

Performance characteristics of electrochromic displays

Eliminating crosstalk in thin film transistor/liquid crystal displays

Eliminating crosstalk in thin-film transistor/liquid-crystal displays

Pressure Dependence of Barrier Heights in Ge-GaAs n—n Heterojunctions